Cell movement in response to specific stimuli is observed to occur in prokaryotes and eukaryotes (Doetsch R N and Seymour W F., 1970; Bailey G B et al., 1985). Cell movement seen in these organisms has been classified into three types: chemotaxis or the movement of cells along a gradient towards an increasing concentration of a chemical; negative chemotaxis which has been defined as the movement down a gradient of a chemical stimulus; and chemokinesis or the increased random movement of cells induced by a chemical agent. The receptors and signal transduction pathways for the actions of specific chemotactically active compounds have been extensively defined in prokaryotic cells. Study of E. Coli chemotaxis has revealed that a chemical which attracts the bacteria at some concentrations and conditions may also act as a negative chemotactic chemical or chemorepellent at others (Tsang N et al., 1973; Repaske D) and Adler J. 1981; Tisa L S and Adler J., 1995; Taylor B L and Johnson M S., 1998).
Chemotaxis and chemokinesis have been observed to occur in mammalian cells (McCutcheon M W, Wartman W and H M Dixon, 1934; Lotz M and H Harris 1956; Boyden S V 1962) in response to the class of proteins, called chemokines (Ward S G and Westwick J; 1998; Kim C H et al., 1998; Baggiolini M, 1998; Farber J M; 1997). Additionally, Poznansky et al. (U.S. Pat. No. 6,448,054 and WO 2004/053165, which are incorporated by reference in their entirety) have observed chemorepellent, or fugetactic, activity in mammalian cells. Improved control over chemotaxis, chemokinesis and fugetaxis, such as in mammalian systems, is desirable.